Antibody against human mucin core protein and method of preparing and using same

ABSTRACT

Antibodies which bind to the core protein of the human polymorphic epithelial mucin glycoprotein are useful in the diagnosis of cancer.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.08/134,992, filed Oct. 12, 1993 (abandoned), which is a continuation ofU.S. patent application Ser. No. 07/381,663, filed Sep. 7, 1989(abandoned), which is the national stage of PCT/GB88/000111, filed Jan.7, 1988, now abandoned, which is a continuation-in-part of U.S. patentapplication Ser. No. 07/041,306, filed Apr. 22, 1987, now abandoned, allhereby incorporated by reference.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to DNA probes for detecting atandemly-repeated nucleotide sequence in the gene encoding mucinglycoprotein expressed by human mammary epithelial cells, to the use ofthe probe in diagnosis and in "fingerprinting" individuals, to thepolypeptides expressed by the corresponding mucin gene, to antibodiesagainst the polypeptides and to the use of the polypeptides andantibodies in the diagnosis and therapeutic treatment of cancer.

BACKGROUND OF THE INVENTION

Normal and malignant human mammary epithelial cells express highmolecular weight glycoproteins (gps) which are extensively glycosylatedand very antigenic. As a result, many of the monoclonal antibodies(MAbs) selected for reactivity with human breast cancer and othercarcinomas are found to react with molecules which are produced inabundance by the fully differentiated human mammary tissue and are foundin the milk fat globule (MFG) and in milk. However, the level ofexpression of a particular antigenic determinant may be different in thegps produced by the normal differentiated cell and in the similarmolecules produced by breast cancers. This means that some antibodiescan show a certain specificity for reacting with tumor gps.

The molecules bearing the epitopes recognized by these antibodies arecomplex and have been difficult to analyze, both because they are largeand heavily glycosylated (>250,000 daltons) and because of the complexpattern of expression. Two of the MAbs, HMFG-1 and -2, react with acomponent in human milk which appears to be greater than 400,000daltons, whereas the molecules found in sera and tumors are smaller,although the dominant components are still greater than 200,000 daltonson immunoblots. The large glycoprotein produced by the differentiatedmammary epithelial cells found in human milk or in the milk fat globulehas been purified and shown to have some of the characteristics of themucins. This component contains a large amount of carbohydrate joined inO-linkage to serine and threonine residues via the linkage sugarN-acetylgalactosamine. Moreover, the core protein contains high levelsof serine, threonine and proline and low levels of aromatic and sulphurcontaining amino acids.

These mucin-like glycoproteins are also secreted by a number of othernormal epithelial cells. The monoclonal antibody HMFG-1 is highlyreactive with the milk mucin and evidence suggests that the epitoperecognized by this antibody is more abundant on the fully processedmucin, characteristic of normal differentiation.

In tumors, the molecular weight of the molecules carrying theseantigenic determinants differs among individual tumors and, in the caseof the components recognized by the HMFG-2 antibody, can range from80-400K daltons. Although it appears that the differences observed inthe mobility of the high molecular weight bands are due to geneticpolymorphism this probably does not explain variations in the size ofthe lower bands. It has been proposed that these may be the result ofaberrant processing occurring in the tumor cell possibly within theglycosylation pathways.

For the majority of the monoclonal antibodies reacting with this groupof molecules the exact nature of the antigenic epitopes remains unclearbut circumstantial evidence has suggested that carbohydrate may at leastbe partly involved in many of the epitopes. Moreover, from previouslyavailable data it was not known whether the mucin found in the normaldifferentiated cells, and that observed in the tumors, contain the samecore protein, or just carry common carbohydrate determinants.

Mucin has now been isolated from human milk by affinity chromatographyenabling identification of the core protein and the gene encoding theprotein. This has been found to be a highly polymorphic gene defined bythe peanut urinary mucin (PUM) locus see Swallow et al., DiseaseMarkers, 4, 247, (1986) and Nature, 327, 82-84 (1987)!. The geneproduct, which is hereafter referred to as human polymorphic epithelialmucin or HPEM, has been detected in breast tumors and other carcinomasas well as in some normal epithelial tissues.

It has now been found that the HPEM core protein has epitopes which alsoappear in the aberrantly processed gps produced by adenocarcinoma cells.Certain of these epitopes are not exposed in the fully processed mucinglycoprotein produced by the lactating mammary gland.

In one aspect the present invention therefore provides an antibodyagainst a human mucin core protein which antibody substantially does notreact with a fully processed human mucin glycoprotein.

As used herein the term "antibody" is intended to include fragments ofantibodies bearing antigen binding sites such as the F(ab')₂ fragments.

SUMMARY OF THE INVENTION

The present invention involves DNA probes for detecting atandemly-repeated nucleotide sequence in the gene encoding mucinglycoprotein expressed by human mammary epithelial cells. The presentinvention also concerns the use of such DNA probes in diagnosis,polypeptides expressed by the corresponding mucin gene, antibodiesagainst the polypeptides, and the use of the polypeptides and antibodiesin the diagnosis and therapeutic treatment of cancer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts the results of the purification of the milk mucin byimmunoaffinity of chromatography using the antibody HMFG-1;

FIG. 2 depicts the results of the comparison of the ¹²⁵ I labelledpurified milk mucin with immunoblot of human skimmed milk;

FIG. 3 depicts the results of autoradiography of the iodinated milkmucin after treatment with hydrogen fluoride;

FIG. 4 depicts the results of reactivity of the intact, partiallystripped or extensively stripped milk mucin with iodinated lectins;

FIG. 5 depicts the results of immunoprecipitation and immunoblots of thepartially and extensively stripped mucin;

FIG. 6a-h depicts the results of reactivity of monoclonal antibodiesSM-3 and HMFG-2 with methacarn fixed breast tissue and tumor sectionsusing an indirect immunoperoxidase staining method;

FIG. 7 depicts the results of periodic acid-silver stained milk mucinafter antibody affinity column and gel filtration column;

FIG. 8 depicts the results of silver stain of partially and totallystripped core protein from milk mucin;

FIG. 9 depicts the results of immunoprecipitation with MAbs of in vitrotranslated protein products from MCF-7 poly(A)⁺ RNA;

FIG. 10 depicts the results of immunoblot analysis of fusion proteinsfrom the λmuc clones;

FIG. 11 depicts the results of hybridization of pMUC10 to cDNA insertsof pMUC clones;

FIG. 12 depicts the results of RNA blot hybridization analysis ofmammary breast mucin mRNA; and

FIG. 13A-B depicts the results of polymorphic human DNA fragmentsdetected by hybridization with pMUC10 probe.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Antibodies according to the present invention react with HPEM coreprotein, especially as expressed by colon, lung, ovary and particularlybreast carcinomas, but have reduced or no reaction with thecorresponding fully processed HPEM. In a particular aspect theantibodies react with HPEM core protein but not with fully processedHPEM glycoprotein as produced by the normal lactating human mammarygland.

Antibodies according to the present invention have no significantreaction with the mucin glycoproteins produced by pregnant or lactatingmammary epithelial tissues but react with the mucin proteins expressedby mammary epithelial adenocarcinoma cells. These antibodies show a muchreduced reaction with benign breast tumors and are therefore useful inthe diagnosis and localization of breast cancer as well as intherapeutic methods.

The antibodies may be used for other purposes including screening cellcultures for the polypeptide expression product of the human mammaryepithelial mucin gene, or fragments thereof, particularly the nascentexpression product. In this case the antibodies may conveniently bepolyclonal or monoclonal antibodies.

Antibodies according to the present invention may be produced byinoculation of suitable animals with HPEM core protein or a fragmentthereof such as the peptides described below. Monoclonal antibodies areproduced by the method of Kohler & Milstein (Nature 256, 495-497/1975)by immortalizing spleen cells from an animal inoculated with the mucincore protein or a fragment thereof, usually by fusion with an immortalcell line (preferably a myeloma cell line), of the same or a differentspecies as the inoculated animal, followed by the appropriate cloningand screening steps.

In a particular aspect the present invention provides the monoclonalantibodies designated SM3 against the HPEM core protein. In anotheraspect the invention provides the hybridoma cell line which secretes theantibodies SM3 and has been designated HSM3. Samples of HSM3 have beendeposited under the Budapest Treaty with European Collection of AnimalCell Cultures (Public Health Laboratory Service, Centre of AppliedMicrobiology and Research, European Collection of Animal Cell Cultures,Porton Down, Salisbury, Silts, England) on Jan. 7, 1987 under accessionnumber 87010701.

This hybridoma cell line will be made available to the public inaccordance with applicable U.S. law and the Budapest Treaty, but thisshould not be construed as conveying a license to make, use or sellsubcultures so obtained.

Using antibodies according to the invention it has been possible toscreen a phage library constructed from mRNA isolated from a humanbreast cancer cell line to identify sequences coding for portions of themucin core protein. Complementary DNA sequences have been constructedand from these it has surprisingly been found that the gene encoding thecore protein contains multiple tandem repeats of a 60 base sequenceleading to considerable polymorphism sufficiently extensive that cDNAfragments corresponding to the repeat sequence would be useful forfingerprinting DNA. The fingerprinting thus made possible hasapplications in for instance ascertaining whether bone marrow growthafter transplants is from the host or the donor and in forensic medicinefor identifying individuals using body tissues or fluids.

Accordingly the present invention also provides a nucleic acid fragmentcomprising at least 17 nucleotide bases the fragment being hybridizablewith at least one of

a) the DNA sequence

    ______________________________________                                        5'                                               *                            ACC  GTG    GGC    TGG  GGG  GGC  GGT  GGA  GCC  CGG--                        GGC  CGG    CCT    GGT  GTC  CGG  GGC  CGA  GGT  GAC--                                                                         *                            ACC  GTG    GGC    TGG  GGG  GGC  GGT  GGA  GCC  CGG--                                                                         3'                           GGC  CGG    CCT    GGT  GTC  CGG  GGC  CGA  GGT  GAC                          ______________________________________                                    

b) DNA complementary to the DNA of a), i.e. of sequence

    ______________________________________                                        5'                                                                            GTC  ACC    TCG    GCC  CCG  GAC  ACC  AGG  CCG  GCC--                        CCG  GGC    TCC    ACC  GCC  CCC  CCA  GCC  CAC  GGT--                        GTC  ACC    TCG    GCC  CCG  GAC  ACC  AGG  CCG  GCC--                        *                                                3'                           CCG  GGC    TCC    ACC  GCC  CCC  CCA  GCC  CAC  GGT                          ______________________________________                                    

c) RNA having a sequence corresponding to the DNA sequence of a) and

d) RNA having a sequence corresponding to the complementary DNA sequenceof b).

The sequences in (a) and (b) each include a double tandem repeatsequence of 120 bases. Fragments according to the invention maycorrespond to any portion of this sequence including portions bridgingthe start point of the repeat.

Fragments according to the invention will hybridize under conditions oflow stringency with the DNA and RNA sequences (a) to (d) above.Preferred fragments are those which also hybridize under conditions ofhigh stringency. The most preferred fragments of the invention are thosewhich have sequences exactly identical to, or exactly complementary tothe sequences (a) to (d) above.

Normally a given DNA or RNA fragment according to the invention will becapable of hybridizing with both DNA according to a) and RNA accordingto c) or with both DNA according to b) and RNA according to d) above.

Preferably the nucleic acid fragment according to the present inventionwill comprise a portion of at least 30 nucleotide bases capable ofhybridizing with at least one of a) to d) above, more preferably atleast 50 such bases and most preferably the fragment contains a sequenceof 60 bases exactly complementary to one of the repeat sequences of a),b) c) or d) above. Other fragments of the invention may comprise two ormore repeats of such a sequence, optionally with minor variations by wayof substitution. Preferably such fragments include an integral number ofsuch repeat sequences. Further fragments of the invention comprise thetandem repeat sequence and additional coding or non-coding 5' and/or 3'flanking sequences corresponding to the HPEM gene or a portion thereof.

When the existence of a tandem repeat sequence was first identified itwas believed that the sequence consisted of 59 base pairs correspondingwith the sequences indicated in (a) and (b) above except for the lack ofthe base indicated with "*".

Many fragments according to the invention as originally defined inBritish Patent Application No. 8700269 also conform with the newdefinition of fragments as set out herein and those fragments ofsequences defined under (a), (b), (c) or (d) above which do not includethe bases marked "," form a particular aspect of the present invention.Such fragments have sequences corresponding to at least a portion of thesequences

a') GTG GGC TGG GGG GGC GGT GGA GCC

a") CGG GGC CGG CCT GGT GTC CGG GGC CGA GGT GAC AC

b') DNA complementary to the sequence of a') or a"),

c') RNA having a sequence corresponding to the sequence of a') or a")and

d') RNA having a sequence corresponding to one of the complementary DNAsequences of b')

In the human genome the DNA tandem repeat sequence comprisesantiparallel double stranded DNA, one strand having sequence (a) andbeing paired with a strand having sequence (b).

As mentioned above the nucleic acid fragments of the invention may beused as a probe for detecting one or other strand of the DNA tandemrepeat sequence in the human genome, or RNA transcribed from eitherstrand and hence for identifying the gene or genes for human mucin coreproteins, mRNA transcribed therefrom and complementary DNA and RNA. Forsuch purposes it may be convenient to use the complete normal genecomprising at least one tandem repeat sequence, or mRNA transcribedtherefrom or to attach non-complementary fragments to either or both the5' and 3' ends of a fragment according to the invention and/or to attachdetectable labels (such as radioisotopes, fluorescent or enzyme labels)to the probe or to bind the probe to a solid support. All of these maybe achieved by conventional methods and the nucleic acid fragments ofthe invention may be produced de novo by conventional nucleic acidsynthesis techniques.

The nucleic acid fragments of the present invention may also be used inactive immunization techniques. In such methods the fragment codes for apolypeptide chain substantially identical to a portion of the mucin coreprotein and may be extended at either or both the 5' and 3' ends withfurther coding or non-coding nucleic acid sequences including regulatoryand promoter sequences, marker sequences and splicing or ligating sites.Coding sequences may code for corresponding portions of the mucin coreprotein chain or for other polypeptide chains. The fragment according tothe invention, together with any necessary or desirable flankingsequences is inserted, in an appropriate open reading frame register,into a suitable vector such as a plasmid or a viral genome (for instancevaccinia virus genome) and is then expressed as a polypeptide product byconventional techniques. In one aspect the polypeptide product may beproduced by culturing appropriate cells transformed with a vector,harvested and used as an immunogen to induce active immunity against themucin core protein. In another aspect the vector, particularly in theform of a virus, may be directly inoculated into a human or animal to beimmunized. The vector then directs expression of the polypeptide in vivoand this in turn serves as an immunogen to induce active immunityagainst the mucin core protein.

The invention therefore provides nucleic acid fragments as hereinbeforedefined for use in methods of treatment of the human or animal body bysurgery or therapy and in diagnostic methods practiced on the human oranimal body. The invention also provides such methods for treatment ofthe human or animal body by surgery or therapy and diagnostic methodspracticed in vivo as well as ex vivo and in vitro.

The invention further provides a polypeptide comprising a series ofresidues encoded by the DNA tandem repeat sequence, the sequence shownat (b) above being the coding sequence. Polypeptides according to theinvention are selected from any of those having 5 or more amino acidresidues represented by the following amino acid sequence Val Thr SerAla Pro Asp Thr Arg Pro Ala Pro Gly Ser Thr Ala Pro Pro Ala His Gly*ValThr Ser Ala Pro Asp Thr Arg Pro Ala Pro Gly Ser Thr Ala Pro Pro Ala HisGly ("*" marks the start of the repeat in the peptide).

Polypeptides according to the invention may have a sequencecorresponding with any portion of the 40 residue sequence above and mayinclude the start point of the repeat sequence.

Other polypeptides according to the invention include three or morerepeats of the 20 amino acid repeat sequence. Such polypeptides mayinclude minor variations by way of substitution of individual amino acidresidues.

The invention further provides polypeptides as defined above modified byaddition of N-acetyl galactosamine (a linkage sugar) on serine and/orthreonine residues and by addition of oligosaccharide moieties to thator via other linkage sugars and/or fragments linked to carrier proteinssuch as keyhole limpet haemocyanin, albumen or thyroglobulin.

Preferably the polypeptide comprises at least 10 amino acid residues ofthe sequence above, more preferably 20 residues. The polypeptide maycomprise the full sequence above. Such polypeptides may further compriseadditional amino acid residues, preferably conforming to the amino acidsequence of HPEM core protein.

In a further aspect the present invention provides the HPEM coreprotein. This is encoded by the PUM gene and may be produced byrecombinant DNA techniques and expressed without glycosylation in humanor non-human cells. Alternatively it may be obtained by strippingcarbohydrate from native human mucin glycoprotein which itself may beproduced by isolation from samples of human tissue or body fluids or byexpression and full processing in a human cell line. The HPEM coreprotein may be used for raising antibodies in animals for use in passiveimmunization, diagnostic tests and tumor localization and in activeimmunization of humans.

The invention further provides antibodies (monoclonal or polyclonal),and fragments thereof, against any of the polypeptides described above.Such antibodies may be obtained by conventional methods and are usefulin diagnostic and therapeutic applications.

The invention further provides antibodies (monoclonal or polyclonal), orfragments thereof, linked to therapeutically or diagnostically effectiveligands. For therapeutic use of the antibodies the ligands are lethalagents to be delivered to cancerous breast or other tissue in order toincapacitate or kill transformed cells. Lethal agents include toxins,radioisotopes and `direct killing agents` such as components ofcomplement as well as cytotoxic or other drugs. Further therapeutic usesof the antibodies inclusive passive immunization.

The invention further provides therapeutic methods comprising theadministration of effective non-toxic amounts of such antibodies orfragments thereof and antibodies or fragments thereof for use intherapeutic treatment of the human or animal body. Especially intherapeutic applications it may be appropriate to modify the antibody bycoupling the Fab region thereof to the Fc region of antibodies derivedfrom the species to be treated (e.g. such that the Fab region of mousemonoclonal antibodies may be administered with a human Fc region toavoid immune response by a human patient) or in order to vary theisotype of the antibody.

In the diagnostic field the antibodies may be linked to ligands such assolid supports and detectable labels such as enzyme labels, chromophoresand fluorophores as well as radioisotopes and other directly orindirectly detectable labels. Preferably monoclonal antibodies orfragments thereof are used in diagnosis.

The invention further provides a diagnostic assay method comprisingcontacting a sample suspected to contain abnormal human mucinglycoproteins with an antibody as defined above. Such methods includetumor localization involving administration to the patient of theantibody or fragment thereof bearing a detectable label or of anantibody or fragment thereof and, separately simultaneously orsequentially in either order a labelling entity capable of selectivelybinding the antibody or fragment thereof. The invention also providesantibodies or fragments thereof for use in diagnostic methods practicedon the human or animal body.

Particular uses of the antibodies include diagnostic assays fordetecting and/or assessing the severity of breast, ovary and lungcancers.

Diagnostic test kits are provided for use in diagnostic assays andcomprise antibody or a fragment thereof, optionally suitable labels andother reagents and, especially for use in competitive assays, standardsera.

The invention will now be illustrated by the following Examples and withreference to the figures of the accompanying drawings.

FIG. 1: Purification of the milk mucin by immunoaffinity chromatographyusing the antibody HMFG-1. Milks from several individuals were combinedand absorbed to a HMFG-1-Sepharose column as described in Methods. Thematerial eluting at low pH was iodinated and subjected to PAGEelectrophoresis and autoradiography (track 1). The iodinated materialwas precipitated using the Protein A method with antibodies HMFG-1(track 5), HMFG-2 (track 2), ST254 (track 3) and RPMI+20% FCS (track 4).

FIG. 2: Comparison of the ²⁵ I labelled purified milk mucin withimmunoblot of human skimmed milk. A, human skimmed milk was subjected toSDS polyacrylamide electrophoresis, transferred to nitrocellulose paper,the blot probed with the monoclonal antibody HMFG-1 and binding detectedusing an ELISA method. B, after purification on an HMFG-1 affinitycolumn followed by G75 Sephadex chromatography the milk mucin wasiodinated by the Bolton and Hunter method and subjected to SDSpolyacrylamide electrophoresis and autoradiography.

FIG. 3: Autoradiography of the iodinated milk mucin after treatment withhydrogen fluoride. The purified milk mucin was treated with HF for 3hours at room temperature (track 1) or 1 hour at 4° C. (track 2) and theresulting preparations were then iodinated and run on SDS polyacrylamidegels.

FIG. 4: Reactivity of the intact, partially stripped or extensivelystripped milk mucin with iodinated lectins. The purified intact milkmucin (track 1), the mucin treated with HF for 1 hour at 4° C. (track 2)and the mucin treated for 3 hours at room temperature (track 3) weresubjected to SDS polyacrylamide electrophoresis and then transferred tonitrocellulose paper. The paper was then probed with ¹²⁵ I PNA (peanutagglutinin), ¹²⁵ I WGA (wheat germ agglutinin), or ¹²⁵ I HPA (Helixpomatia agglutinin).

FIG. 5: Immunoprecipitation and immunoblots of the partially andextensively stripped mucin. A, the ¹²⁵ I extensively stripped mucin wasimmunoprecipitated with SM-3 (track 3), HMFG-2 (track 2) or NS2 mediumas a control (track 1) by the protein A plate method (see Materials andMethods). B, the partially stripped mucin (track 1) or extensivelystripped mucin (track 2) was run on SDS polyacrylamide gels andtransferred to nitrocellulose paper. The blot was then reacted with acocktail of SM-3 and SM-4 monoclonal antibodies and the binding detectedusing an ELISA method.

FIG. 6: Reactivity of monoclonal antibodies SM-3 and HMFG-2 withmethacarn fixed breast tissue and tumor sections using an indirectimmunoperoxidase staining method. Infiltrating ductal carcinoma showingstrong reactivity with both SM-3 (A) and HMFG-2 (B). Fibroadenomashowing no reactivity with SM-3 (C) and strong heterogeneous staining ofthe epithelium with HMFG-2 (D). Papilloma showing very weak reactivitywith SM-3 (E) and strong positivity with HMFG-2 (F). Both normal restingbreast (G) and lactating breast (J) were negative when stained withSM-3, whereas both tissues stained positively with HMFG-2 with lactatingbreast much stronger than normal resting breast (H).

FIG. 7. Periodic acid-silver stained milk mucin after antibody affinitycolumn and gel filtration column. Milk mucin was purified on an HMFG-1antibody affinity column (lane 1) followed by passage through a G75Sephadex column (lane 2), subjected to NaDodSO₄ /polyacrylamide gelelectrophoresis, and silver stained following treatment of gels with0.2% periodic acid.

FIG. 8 Silver stain of partially and totally stripped core protein frommilk mucin. The purified milk mucin was deglycosylated by treatment withanhydrous hydrogen fluoride for 1 hr at 0° C. (lane 1) and 3 hr at roomtemperature (lane 2), separated by electrophoresis through a NaDodSO₄/polyacrylamide gel (10%) and silver stained.

FIG. 9. Immunoprecipitation with MAbs of in vitro translated proteinproducts from MCF-7 poly(A)⁺ RNA. Poly(A)⁺ RNA from MCF-7 cells wastranslated in a rabbit reticulocyte lysate system (Amersham) in thepresence of ³⁵ S!methionine (1000 Ci/mmole; 1Ci=37 GBq) following themanufacturer's conditions. Samples containing 5×10⁴ acid precipitablecpm were precipitated with MAbs SM-4 (lane 1), SM-3 (lane 2), HMFG-2(lane 3), HMFG-1 (lane 4) and an irrelevant MAb to interferon (lane 5,24), separated on a NaDodSO₄ /polyacrylamide gel (10%), impregnated withAmplify and exposed to XAR-5 film at -70° C., for 20 days.

FIG. 10. Immunoblot analysis of fusion proteins from the λmuc clones.The phage clones λMUC 3,4,6,7,8,9 and 10 were used to lysogenizebacterial strain Y 1089. Lysogens were grown at 32° C., shifted to 42°C., and then induced with IPTG. Lysogen proteins were fractionated byelectrophoresis through a NaDodSO₄ /polyacrylamide gel (7.5%),transferred to nitrocellulose, and reached with HMFG-2. The binding wasdetected with an ELISA method using 4-chloro-1-naphthol as thesubstrate. The numbers are those of the λ clones.

FIG. 11. Hybridization of pMUC10 to cDNA inserts of pMUC clones. DNAfrom the plasmid clones was digested with restriction enzyme EcoRI toexcise the cDNA inserts, separated by electrophoresis on 1.4% agaroseand transferred to Biodyne nylon membrane. The filter was hybridizedusing standard conditions (34) to the insert from pMUC10 which waslabelled with α-³² p!dCTP by the method of random priming (41). Lanes:plasmid clones 3, 4, 6, 7, 8, 9, 10.

FIG. 12. RNA blot hybridization analysis of mammary breast mucin mRNA.10 μg of total RNA from human breast cancer cells MCF-7 (lane 1) andT47D (lane 2), normal human mammary epithelial cells HuME (lane 3),human embryonic fibroblasts ICRF 23 (lane 4), Daudi cells (lane 5) andcarcinosarcoma HS578T cells (lane 6) were separated in a 1.3%agarose/glyoxal gel, blotted on to nitrocellulose and hybridized to thepMUC10 EcoRI insert which was labelled with α-³² p!dCTP by the method ofrandom priming (41). The size markers were 28S (5.4kb) and 18S (2.1kb)rRNAs.

FIG. 13. Polymorphic human DNA fragments detected by hybridization withpMUC10 probe. Genomic DNA samples prepared from the white blood cellsfrom ten individuals (six unrelated) and from three cell lines weredigested to completion with HinfI and EcoRI, fractionated byelectrophoresis through 0.7% and 0.6% agarose, respectively, andtransferred to Biodyne nylon membranes. The filter way hybridized to thepMUC10 DNA insert which was labelled with a³² p!dCTP by the method ofrandom priming (41). X-ray film was exposed for 1 day at -70° C. withintensifying screens. Lanes 1-4 father, two daughters and mother, lanes5-10 unrelated individuals, lane 11 is MCF-7, lane 12 is ZR75-1, lane 13is ICRF-23. The DNA samples exhibit a wide distribution of sizes.Numbers indicated length of DNA in kb. The apparent bands at 23Kb are inlanes 12 and 13 are artifacts introduced in autoradiography.

Abbreviations

The abbreviations used are: HMFG, human milk fat globule; PBS,phosphate-buffered saline (153 mM NaCL, 3 mM KCL, 10 mM Na₂ HPO₄, 2 mMKM₂ PO₄ pH 7.4); WGA, wheat germ agglutinin; PNA, peanut agglutinin;HPA, Helix pomatia agglutinin; BSA, bovine serum albumin; SDS, sodiumdodecyl sulfate; MAb, monoclonal antibody; IPTG, isopropylβ-D-thiogalactoside; bp, base pair(s); Kb, kilobase(s).

EXAMPLE 1

Purification of the milk mucin

The milk mucin was purified from human skimmed milk by passage throughan HMFG-1 affinity column followed by size exclusion chromatography. TheHMFG-1 monoclonal antibody was purified from tissue culture supernatantusing a protein A column (1). The purified antibody was coupled tocyanogen bromide activated sepharose (Pharmacia) as described in themanufacturer's instructions. Human skimmed milk was passed in batches of100 ml through the antibody column followed by extensive washing withPBS. Bound antigen was eluted from the column using 0.1 M glycine pH 2.5and the fractions registering an optical density at 280nm were pooled,dialyzed against 0.25 M acetic acid and lyophilized. Batches of about 20mgs were dissolved in 0.25 M acetic acid and passed through a G75Sephadex column (1×100 cm) which had been previously equiligrated withacetic acid. The column was washed with 0.25 M acetic acid and 1 mlfractions collected. The peak fractions which were eluted in the voidvolume were pooled, lyophilized and the dry powder stored at 4° C. Aminoacid analysis was performed using a Beckman 6300 amino acid analyzer.

Deglycosylation of the milk mucin

To remove the O-linked carbohydrate from the milk mucin the molecule wastreated with anhydrous hydrogen fluoride as described by Mort andLamport (21), for either 1 hour at 4° C. which produced a partiallystripped preparation, or 3 hours at room temperature which produced theextensively stripped mucin.

Iodination of the milk mucin

Iodinations of the purified mucin, the partially or extensively strippedmucin were carried out using the Bolton and Hunter method (51). Briefly,the mucin, 2.5 μg in 20 μl 0.1M borate buffer pH 8.5, was added to thedried Bolton and Hunter reagent (1 mCi, Amersham International plc) andincubated at room temperature for 15 minutes. The reaction was stoppedby the addition of 0.5 ml of 0.2M glycine in borate buffer and after afurther 15 minutes incubation, free Bolton and Hunter reagent wasremoved by passage through a G25 Sephadex column (PD10 columns,Pharmacia) previously equilibrated in PBS.

Iodination of Lectins

Wheat germ agglutinin (WGA), peanut agglutinin (PNA) (Vector Labs) andHelix pomatia agglutinin (HPA) (Boehringer) were iodinated as describedby Karlsson et al. (52) using the chloramine T method.

Polyacrylamide gels and Western blots

Polyacrylamide gel electrophoresis and immunoblotting was performed asdescribed previously (1). Briefly, samples were run on 5-15%polyacrylamide gels and then electrophoretically transferred tonitrocellulose paper (Schleicher and Schuell) at 50 volts overnight at4° C. (36). In the immunoblotting experiments the paper was reacted withmonoclonal antibodies and binding detected with an ELISA method using4-chloro-1-naphthol as the substrate. For lectin binding studies theWestern blots were reacted with the iodinated lectins as described bySwallow et al. (48).

Production of monoclonal antibodies

A female BALB/c mouse was immunized with 5 μg of the partially strippedmilk mucin in Freund's complete adjuvant and 3 months later boosted witha further 5 μg of the same preparation of Freund's incomplete adjuvant.After a further 20 days, 5 μg of the mucin extensively stripped of itscarbohydrate was given intravenously in saline solution. The spleen wasremoved 4 days later, and fused with the NS2 mouse myeloma cell line(53).

Screening of hybridoma supernatant and immunoprecipitations

The screening assay was a modification of that described by Melero andGonzalez-Rodriguez (54). Multiwell plates were coated with 50 μl of 0.1mg/ml protein A (Pharmacia Fine Chemicals) in PBS and allowed to dryovernight at 37° C. The plates were blocked with 5% BSA for 1 hour at37° C. followed by the addition of 50 μl of rabbit anti-mouseimmunoglobulin (DAKO, diluted 1:10 in PBS/BSA=PBS/BSA). After incubatingfor 2 hours at 37° C. the plates were washed twice with PBS containing1% BSA and 50 μl of hybridoma supernatant added. The plates wereincubated overnight at 4° C., washed twice with PBS/BSA and 50 μl ofiodinated partially stripped mucin containing 100,000 cpm added to eachwell. The plates were then incubated at room temperature for 4 hours,washed 4 times with PBS/BSA and the individual wells counted in a gammacounter. For immunoprecipitation experiments 50 μl of SDS sample buffercontaining dithiothreitol was added to each of the wells which were thenboiled for 3 minutes and the buffer loaded onto 5-15% polyacrylamidegradient gels.

Staining of tissue sections

Tissues from primary mammary carcinomas, benign breast biopsies, normalbreast, and pregnant lactating breast tissue were fixed in methacarn(methanol chloroform and acetic acid 60:30:10) and embedded intoparaffin wax. Sections were stained with the antibodies using theindirect peroxidase anti peroxidase method as previously described (47).

Purification of the milk mucin

The milk mucin was purified from human skimmed milk on an HMFG-1antibody affinity column. Iodination of the eluted material revealed thepresence of a large molecular weight component and a 68KD band.Precipitation of the affinity purified material with antibodies HMFG-1and HMFG-2 (FIG. 1 tracks 2 and 5) followed by gel electrophoresisshowed that both the high molecular weight components and the 68KDcomponent were precipitated by both antibodies (less effectively byHMFG-2). Since the 68KD component was also precipitated by two unrelatedantibodies (FIG. 1, tracks 3 and 4) and this component was not evidenton an immunoblot of the purified material reacted with HMFG-1 (FIG. 2A),the 68K component was removed by molecular sieve chromatography on a G75column. The final purified product showed a major high molecular weightband, with only a trace of the 68K component and a minor contaminantaround 14K (FIG. 2B).

A high molecular weight glycoprotein (PAS-O) containing more than 50%carbohydrate in O-linkage has been purified from the human milk fatglobule by Shimizu and Yamauchi (8). To see whether this component wassimilar to the mucin isolated from milk by affinity chromatography on anHMFG-1 affinity column, the amino acid composition of the purifiedHMFG-1 reactive mucin was determined and compared to the amino acidcomposition of the purified PAS-O component. Table 1 shows that there isgood correspondence between the two sets of data, indicating that thecore proteins of PAS-O and the mucin purified here are the same.

                  TABLE 1                                                         ______________________________________                                        Amino acid composition of the human milk mucin -                              comparison with PAS-O                                                                 HMGF-1      Extensively                                                                             PAS-9                                           Amino   purified    stripped  (Shimizu &                                      acid    milk mucin  milk mucin                                                                              Yamauchi 1982)                                  ______________________________________                                        Asp     6.1         7.2       6.4                                             Thr     9.4         9.7       9.8                                             Ser     9.1         13.0      13.1                                            Gly     6.3         9.6       8.3                                             Pro     14.8        14.4      12.0                                            Gly     8.1         10.1      12.2                                            Ala     12.3        11.9      13.0                                            Cys     Not analyzed                                                                              Not analyzed                                                                            0.5                                             Val     6.0         6.3       5.3                                             Met     0.5         0.4       0.8                                             Ile     1.6         1.7       1.9                                             Leu     4.5         4.8       3.7                                             Tyr     2.0         0.9       1.6                                             Phe     2.0         1.6       1.7                                             His     3.2         2.3       3.8                                             Lys     2.8         3.3       2.2                                             Arg     4.0         4.0       3.9                                             ______________________________________                                    

Isolation of the core protein of the milk mucin

As there are no enzymes easily available that are efficient at removingO-linked sugars, and β elimination often results in damage to theprotein core, the oligosaccharides were removed by treatment of themucin with anhydrous hydrogen fluoride. This treatment has been shown byMort and Lamport (21) to be effective in removing sugars from pigsubmaxillary mucin without damaging the protein core. Amino acidanalysis of the material produced after HF treatment of the milk mucinsuggested that the protein core was also in this case undamaged, sincethe composition was the same as that seen in the intact mucin (Table 1).

Initially the milk mucin was exposed to HF for only 1 hour at 4°, butanalysis of the product showed that there was only partial removal ofthe sugars with such treatment, and it was necessary to treat the mucinat room temperature for 3 hours to obtain a molecule which showed nolectin binding ability. FIG. 3 shows an autoradiograph of the iodinatedproducts after treatment for 1 hour at 4° (track 2) or 3 hours at RT(track 1). It can be seen from FIG. 3 that the milder treatment resultsin a mixture of products made up of high molecular weight material whichis slightly smaller than the intact mucin and a number of smaller bands.After longer exposure to HF at room temperature, the high molecularweight bands disappeared resulting in polypeptide bands of about 68KDand 72KD.

To test for the presence of sugars on the intact mucin and on theproducts produced after the two different HF treatments each preparationwas subjected to acrylamide gel electrophoresis, transferred tonitrocellulose paper and reached with ¹²⁵ I-labelled lectins. Thelectins used were peanut lectin (PNA) which reacts with galactose linkedto N-acetyl galactosamine, wheat germ (WGA) reactive with N-acetylglucosamine and Helix pomatia agglutinin (HPA) which reacts with thelinkage sugar in O-linked glycosylation, N-acetylgalactosamine. FIG. 4shows autoradiographs of the reacted blots, and it can be seen thatwhile treatment with HF for 1 hr at 4° (track 2) alters the lectinreactivity of the mucin, carbohydrate is still present. Interestingly,however, there is a much lower level of binding of PNA to the highmolecular weight material of the partially stripped mucin than is seenwith the intact mucin (track 1). Moreover, this loss in PNA bindingability is accompanied by binding of the linkage sugar specified lectinHPA. This lectin shows no binding at all to the intact mucin, and thechanged pattern of lectin binding after limited treatment with HFindicates that sugars masking the O-linked N-acetylgalactosamine havebeen stripped off. The smaller component seen in both the intact mucin(track 1) and in the partially stripped preparation (track 2) is aglycoprotein which reacts with WGA, although not with PNA. This maycorrespond to the component of similar molecular weight (around 68K)seen after affinity chromatography of the mucin and may represent anintermediate precursor molecule.

FIG. 4 shows clearly that the 68K and 72K components produced afterextensive treatment with HF (3 hr at RT), show no reactivity with thelectins (track 3), including the N-acetylgalactosamine specific lectinHPA. This observation constitutes strong evidence that the sugars havebeen removed from at least the majority of the molecules, and we willrefer to this preparation as the extensively stripped mucin.

Generation of monoclonal antibodies to the milk mucin core protein

A fusion was carried out using the spleen of a mouse that had beenimmunized with two injections of the partially stripped milk mucinfollowed by a boost with the extensively stripped mucin. The clones wereinitially screened against the ¹²⁵ I partially stripped material usingprotein A plates (see Methods). Four hybridomas were selected andcloned, and Table 2 shows their spectrum of reactivity with the intact,partially and extensively stripped mucin. As can be seen from this tablethree of the hybridomas which were isolated showed a strong reactionwith the partially and extensively stripped mucin and did not react withthe intact mucin. These appeared to be good candidates for monoclonalantibodies to the protein core and two, SM-3 and SM-4, were selected tobe characterized further.

It can also be seen from Table 2 that the HMFG-1 and HMFG-2 antibodiesreacted very strongly with the mucin stripped of its carbohydrate. Thesetwo antibodies were, in fact, developed using the intact mucin (from themilk fat globule) as immunogen and, in the case of HMFG-2, growingmammary epithelial cells (14). Their reaction with the stripped mucinwas unexpected, as circumstantial evidence had previously led to thebelief that carbohydrate might form at least part of their antigenicepitopes.

                  TABLE 2                                                         ______________________________________                                        Reactivity of the antibodies on intact, partially and                         totally deglycosylated milk mucin                                                    .sup.125 I cpm bound                                                                        Partially   Totally                                      Antibody Intact molecule                                                                           stripped mucin                                                                            stripped mucin                               ______________________________________                                        5.17     8,524       11,925      5,780                                        9.13     525         3,000       3,328                                        SM-3     465         15,414      9,200                                        SM-4     816         16,750      9,561                                        HMFG-1   32,000      33,768      9,494                                        HMFG-2   29,500      29,230      15,832                                       NS2 medium                                                                             397         845         650                                          ______________________________________                                    

The binding of antibodies to iodinated intact, partially and totallydeglycosylated milk mucin was assayed using the protein A plate methodas described in Materials and Methods.

Molecular Weight of molecules carrying antigenic determinants

The antibody SM-3 was shown to be of the IgG1 subclass, while the SM-4antibody was found to be IgM. We therefore chose to use the SM-3antibody in subsequent experiments since antibodies of the IgM class canpresent problems in some application. Immunoprecipitation of theextensively stripped material with SM-3 showed a reaction with thelectin unreactive 68K component (FIG. 5A, track 3). The monoclonalantibody HMFG-2 can also be seen to immune precipitate thelectin-unreactive 68K component (track 2). The antibodies were reactivewith antigen on immunoblots and FIG. 5B shows the reaction of antibodySM-3 with the dominant 68K band of the extensively stripped mucin (track2).

We have previously shown that the molecular weight of the components inbreast cancer cells carrying determinants found on the milk mucin islower than 400K and can vary from one tumor to another (1). Reaction ofantibody SM-3 with Western blots of gel separated extracts of breasttumor cells shows that this antibody reacts with components of similarmolecular weight to those reactive with antibody HMFG-2 (data notshown). Because the antibody SM-3 differs from the antibodies HMFG-1 and2 in that it does not react with the intact mucin processed by thelactating gland and yet reacts with molecules processed by breast cancercells, it was appropriate to examine the reaction of SM-3 with a rangeof breast cancers.

Reactivity of SM-3 with breast tissues and tumors

The antibody SM-3 reacted with paraffin embedded tissues provided thesewere fixed in methacarn (not formal saline). Using this method forpreparation of tissue sections, the reaction of the antibody wascompared to that of HMFG-2 on breast tissues and tumors with an indirectimmunoperoxidase staining method. This analysis showed a dramaticdifference in the staining pattern of SM-3 compared to that seen withHMFG-2. Thus, although a strong positive reaction was seen in 20/22breast cancers stained with SM-3 (as compared to 22/22 stained withHMFG-2), normal resting breast, pregnant or lactating tissues and mostbenign lesions were largely unstained with SM-3 but were stained withHMFG-2. Some examples of staining patterns of breast tissues and tumorsare illustrated in FIG. 6.

Twenty-two primary carcinomas and fourteen benign lesions were examinedand the reaction of SM-3 compared to the staining with HMFG-2 in eachcase. In the primary carcinomas, staining with SM-3 was heterogeneousbut generally quite strong and always confined to tumor cells;connective tissue and stroma showed no reaction (see FIGS. 6A,B). In thefour fibroadenomas examined, staining of the epithelium with HMFG-2 wasstrong although heterogeneous. In comparison, staining with SM-3 wasnegative in one case and in the three others staining was confined toonly one or two glandular elements. HMFG-2 showed strong positivity ofthe five papillomas and five cases of cystic disease studied while thestaining observed with SM-3 was very much weaker and more heterogeneous(FIGS. 6G,H). The papillomas as a group showed the strongest stainingwith SM-3, and it can be seen that the staining was membranous orextracellular.

In contrast to HMFG-1 and HMFG-2 which strongly stain lactating andpregnant breast, SM-3 was totally negative with three out of six casesof pregnant or lactating breast (see FIGS. 6C and D). Two positive casesshowed only very weak staining of an occasional cell and in the third,staining was confined to two areas of one lobule. Again, in contrast toHMFG-1 and HMFG-2 which do react with some terminal ductal lobular unitsof normal, resting breast (albeit weakly), SM-3 was totally negative oneight out of the thirteen cases tested and in the other five casesstaining was extremely weak and often confined to one or two acini inthe tissue section (see FIGS. 6E and F). It should perhaps be noted thatthe intensity of staining with HMFG-2 seen with normal breast tissuesand benign lesions fixed in methacarn was somewhat higher than thatreported previously using formalin fixed material (50, 47).

SM-3 was also shown to be negative on sections of normal liver, lung,thymus, sweat gland, epididymis, prostate, bladder, small intestine,large intestine, appendix, thyroid and skin. The antibody showed weakpositive staining only with the distal tubules of the kidney, theoccasional chief cell of the stomach, the occasional duct cell of thesalivary gland and the sebaceous gland.

Discussion

Large molecular weight mucin molecules are expressed by many carcinomasand carry many of the tumor associated antigenic determinants recognizedby monoclonal antibodies. These epitopes may also be expressed by somenormal epithelium, and some monoclonal antibodies like HMFG-1 reactparticularly well with a mucin found in normal human milk (1,17). Aslong as the study of the mucins is restricted to their detection withantibodies reactive with undefined epitopes, the knowledge of theirstructure, expression and processing with also be restricted. We havebegun to investigate the structure and expression of the mammary mucinby isolating the core protein and developing antibodies which haveallowed us to select partial cDNA clones for the gene coding for thecore protein. This Example describes the production and characterizationof these antibodies.

Treatment of the HMFG-1 affinity purified milk mucin with hydrogenfluoride resulted in the appearance of a dominant band of about 68Kdaltons and a minor species of about 72KD on SDS acrylamide gels. Thesebands showed no reactivity with lectins, including Helix pomatiaagglutinin which is specific for N-acetyl galactosamine, the first sugarin O-linked glycosylation (55). It therefore seems probable that this68K dalton polypeptide represents the core protein of the mucin.Supportive evidence for this comes from the observation that theantibodies described here, which are reactive with the stripped 68Kcomponent, can precipitate a molecule of this size from the in vitrotranslation products of mRNA isolated from breast cancer cellsexpressing the mucin.

As the milk mucin contains at least 50% carbohydrate(16), a protein coreof only 68KD appears too small if the intact molecule has an observedmolecular weight greater than 400KD. However, mucins can be composed ofsmall subunits which aggregate and are held together by some form ofnon-covalent interactions, as yet not understood. For example, althoughthe molecular weight of the ovine submaxillary mucin has been reportedto be greater than 1×10⁶ daltons (45), it has a protein core of only 650amino acids with a molecular weight of 58,300 daltons (46).

An unexpected finding was that the antibodies HMFG-1 and HMFG-2 whichreact with the milk mucin, also show a positive reaction with theextensively stripped material which showed no lectin binding capability.Previous indirect evidence, including the resistance to fixation,boiling and reduction, the repetitive nature of their epitopes and theappearance of several bands on immunoblots, had led to the belief thatcarbohydrate present on the milk mucin was involved in these epitopes.This idea was reinforced by the observation that lectin could block thebinding of HMFG-1 and 2 (1). While it is not possible to exclude thepossibility that some sugars, undetected by the lectin bindingexperiments, remain on the extensively stripped mucin described here,this is unlikely to be the explanation for the reactivity of theantibodies HMFG-1 and 2. This can be said since both antibodies haverecently been shown to react positively with β-galactosidase fusionproteins expressed by phage carrying DNA coding for the core protein ofthe mammary mucin. It appears therefore that at least part of each ofthe epitopes recognized by HMFG-1 and HMFG-2 contain amino acids but itmust be assumed that some of these epitopes on the core protein areexposed, i.e. not masked in the fully glycosylated molecule. The HMFG-2epitope is however less abundant on the milk mucin than the HMFG-1epitope, while it is readily detectable on the mucin molecules expressedby tumors (1). These molecules have a smaller molecular weight and maybe less heavily glycosylated or polymerized.

Here we have reported the development of new antibodies which arereactive with the protein core of the mucin and with the partiallydeglycosylated molecule, but which are unreactive with the fullyprocessed mucin produced by the lactating mammary gland. One of theseantibodies SM-3, which is IgG1, has been studied in more detail. It hasbeen shown to react with the mucin molecules which are produced bybreast cancer cells and are recognized by many antibodies developedagainst the intact milk mucin. It should be emphasized however that theepitope recognized by SM-3 which is on the core protein and is exposedin the mucin as processed by tumor cells, is not exposed on the normalmilk mucin. This feature offers the possibility of enhanced tumorspecificity, and a pilot immunohistochemical study of breast tumors andtissues has shown that indeed the SM-3 antibody reacts strongly with themajority of primary breast cancers (91%) but shows little or no reactionwith benign breast tumors, resting or lactating breast, and most normaltissues.

There are several implications of the work described here which may beimportant for both basic and clinical studies in breast cancer. Theobservation that parts of the core protein (detectable by antibodies)are exposed on the mucins as processed by breast cancer but masked onthe mucin as processed by cells in normal breast and benign tumorsimplies that there is an alteration in the processing of the mucin inmalignancy. A more detailed study of the processing of the mucin innormal and malignant cells may then give basic information for definingthe malignant cell. Moreover, since the specificity of the reaction ofthe antibody SM-3 for tumors is better than that of antibodies developedagainst the intact mucin, this antibody may prove to be a more effectivediagnostic tool for the detection of breast cancer cells in tissuesections, tissue fluids and cells. The reactive components are membraneassociated as well as intracellular and in vivo localization of tumorsmay also be possible.

EXAMPLE 2

Purification and deglycosylation of human milk mucin was conducted as inExample 1 mucin was purified on an HMFG-1 antibody.

The stripped mucin preparations were separated by electrophoresisthrough NaDodSO₄ /polyacrylamide gels (10%) and silver stained by twomethods, one of which can be used to stain highly glycosylated proteins(22,23).

Preparation of polyclonal rabbit antiserum to stripped core protein

One New Zealand White rabbit was immunized with 100 μg of the partiallystripped core protein in complete Freund's adjuvant (Gibco). Boosterinjections of 500 μg of the totally stripped core protein wereadministered in incomplete Freund's adjuvant (Gibco) 3 and 4 weeks afterthe initial injection and the rabbit was bled one week later. Tenmicroliters of immune serum (75 μg/ml protein) precipitated 200 ng offully stripped core protein in a Protein A assay (24) and detected it onimmunoblots. The immunoglobulin fractions of rabbit preimmune and rabbitanti-mucin core protein were prepared by adding ammonium sulfate to 50%saturation. The resulting pellet was resuspended in one-half theoriginal serum volume of PBS and dialyzed against the same buffer. Afterdialysis, only residual precipitate was removed by centrifugation.Immunoglobulin fractions were stored in aliquots at -20° C.

Description of MAbs used

In addition to the polyclonal antiserum used for initial screening, acocktail of two MAbs, SM-3 and SM-4 (see Example 1) which recognize themucin core protein (20) and HMFG-1 and HMFG-2 (1, 14) were used toscreen the purified plaques, the β-galactosidase fusion proteins and forimmunoprecipitations from in vitro translated proteins. (The MAbs SM-3and SM-4 (SM refers to stripped mucin) show strong reactivity with thepartially and fully stripped core protein but no reactivity with thefully glycosylated mucin (20).) Other MAbs used were a monoclonalanti-β-galactosidase antibody (25) which was a gift from H. Durbin(ICRF, London), an anti-interferon antibody, ST254 (24), LE61, a keratinantibody (26) and M18 which recognizes a carbohydrate structure on themilk mucin (27).

In vitro translation of proteins

RNA was isolated from the human breast cancer cell line MCF-7 using theguanidium isothiocyanate method of Chirgwin et al. (28) and poly(A)⁺ RNAwas purified by chromatography using oligo (dT)-cellulose (New EnglandBio Labs). The poly(A)+RNA was translated in a reticulocyte lysatesystem (Amersham) in the presence of ³⁵ S! methionine (1000 Ci/mmole; 1Ci=37 CBq, Amersham). Samples containing 5×10⁴ acid insoluble cpm wereprecipitated in a protein A assay (24) using MAbs SM-3, SM-4, HMFG-1,HMFG-2 and a control antibody to human interferon. The antibody-selectedproteins were then separated on a 10% NaDodSO₄ /polyacrylamide gel,impregnated with Amplify (Amersham) and exposed to XAR-5 film (Kodak) at-70° C.

Antibody screening of λgt11 library and protein blotting

The λgt11 library used in this study was constructed from mRNA isolatedfrom the human breast cancer cell line MCF-7 and was generously providedby Philippe Walter and Pierre Chambon (Strasbourg, France). The poly(A)⁺RNA used for the preparation of the randomly primed library was preparedfrom mRNA that sedimented faster than 28S rRNA and was enriched inestrogen receptor (29). The library was made essentially as described byHuynh et al. and Young and Davis (30-32) and contained approximately1×10⁶ recombinants per μg of RNA. Between 85% and 95% of the plaquescontained inserts.

The phage library was plated onto bacterial strain Y1090 and grown for 3hr at 42° C. After isopropyl β-D-thiogalactoside (IPTG) induction and 3hr of growth at 37° C., filters were prepared from each plate andscreened with anti-mucin core protein antibody by the method of Youngand Davis (32). The first antibody used in screening was the rabbitantiserum raised against the stripped core protein prepared as describedabove. Prior to use in screening, the antiserum was diluted 1:200 in PBScontaining 1% bovine serum albumin (PBS/BSA). Preasborption with Y1090bacterial lysate was not found to be necessary. The nitrocellulosefilters (Schleicher and Schuell) were blocked by incubation in PBScontaining 5% BSA for 1 hr at room temperature with gentle agitation.The filters were incubated at room temperature overnight with a 1:200dilution of antiserum in heat sealed plastic bags. The filters werewashed 5×5 min in PBS/BSA, and bound antibody was detected by usinghorseradish peroxidase-conjugated sheep anti-rabbit antiserum (Dako)diluted 1:500 with PBS/BSA and incubated for 2 hr with the filters. Thefilters were washed 5×5 min in PBS/BSA and 1×10 min in PBS before colordetection using 4-chloro-1-naphthol (1). Immunoreactive bacteriophagewere picked and purified through two additional rounds of screening.Subsequently, bacteriophage inserts were subcloned into the EcoRI sitesof pUC8 (33) producing the plasmid used most extensively, pMUC 10. Theplasmids were maintained in DH1 cells.

To examine the B-galactosidase-cDNA fusion proteins forimmunoreactivity, cell lysates were derived. Lysogens were prepared asdescribed in Young and Davis (34). Cells were pelleted, suspended inLaemmli sample buffer (35) and separated by electrophoresis throughNaDodSO₄ /polyacrylamide gels (10%) and transferred onto nitrocellulosefilters as described (1, 36). The filters were treated as above forantibody screening.

Northern Analysis

RNA was isolated from tissue culture cells and frozen tissues by theguanidinium isothiocyanate method of Chirgwin et al. (28). Total RNA (10μg per lane) was denatured by heating at 55° C. for 1 hr in deionizedglyoxal and fractionated by electrophoresis through a 1.3% glyoxal gel(38). The RNA was transferred to nitrocellulose (Schleicher andSchuell), prehybridized and hybridized as described by Thomas (34).Filters were washed down to 0.1X SSC with 0.1% SDS at 65° C. and exposedto XAR-5 film (Kodak) at -70° C. with intensifying screens.

Southern analysis

High molecular weight genomic DNA was prepared from white blood cellsand cell lines (39, 40). These genomic DNAs (10 μg) were cleaved withrestriction enzymes following the manufacturer's recommended conditionsand fractioned through 0.6% and 0.7% agarose gels. Cloned plasmid DNAwas cleaved and fractionated on 1.3% agarose. The gels were denatured,neutralized and transferred to nylon membranes (Biodyne) according tothe manufacturer's instructions. The EcoR1 insert from pMUC10 wasseparated on a 1% low melting point agarose (Biorad) gel and labelledwith α-³² P!dCTP by the method of random priming (41) and hybridized tofilters at 42° C. Filters were washed down to 0.1X SSC with 0.1% SDS at55° C. and exposed to XAR-5 film (Kodak) at -70° C. with intensifyingscreens.

Purification and deglycosylation of mucin glycoprotein

Mucin glycoprotein reactive with the monoclonal antibody HMFG-1 wasprepared from pooled human breast milk by using an HMFG-1 antibodyaffinity column, followed by molecular sieve chromatography on SephadexG-75 in order to remove lower molecular weight components (FIG. 7, lane1). In order to demonstrate the homogeneity of the purified molecule,amino acid analyses of four separate preparations were performed andrevealed a fairly consistent composition with serine, threonine,proline, alanine and glycine accounting for 58% of the amino acids.Periodic acid silver stained gels revealed a diffuse band of greaterthan 400,000 daltons visible only when the gel was treated with periodicacid before the silver stain (FIG. 7, lane 2). No other lower molecularweight bands were visualized on the gel using the silver stain withoutprior treatment with periodic acid.

The purified material was subjected to treatment with hydrogen fluorideto remove the O-linked sugars that are characteristic of mucinglycoproteins. Two different reaction conditions were used whichresulted in a partially deglycosylated core protein (treated at 0° C.for 1 hr) and a fully deglycosylated core protein (treated at roomtemperature for 3 hr) as determined by iodinated lectin bindingfollowing separation by gel electrophoresis and transfer tonitrocellulose paper (20). The partially deglycosylated core protein wasreactive with wheat germ agglutinin, peanut agglutinin and helixpommatia lectin (which recognizes the linkage sugarN-acetylgalactosamine) whereas the fully stripped protein showed noreactivity with any of these three lectins.

The hydrogen fluoride treated core protein was separated byelectrophoresis through NaDodSO₄ /polyacrylamide gels (10%) and silverstained. Silver staining revealed that the predominant component of thepartially strapped mucin was a high molecular weight band of about 400kd, although faint bands of lower molecular weight could also beobserved (FIG. 8, lane 1). Since the high molecular weight materialshowed a somewhat increased mobility in the gel and reacted with thelectin recognizing the linkage sugar, it can be assumed that some sugarshad been removed. The fully stripped mucin consisted of two bands ofabout 68 kd and 72 kd (FIG. 8, lane 2).

Antibody reactive proteins produced by MCF-7 cells

The MCF-7 breast cancer cell line expresses large amounts of HMFG-1 and-2 reactive material on its cell surface (14) and was thus judged to bea suitable source of mRNA for a cDNA library. Before proceeding toscreen the MCF-7 library with the monoclonal antibodies, they weretested for their ability to precipitate a component from in vitrotranslation products produced from MCF-7 mRNA. Poly(A)⁺ RNA from MCF-7was prepared and translated in vitro. Proteins from the translationreaction were immunoprecipitated using the monoclonal antibodies HMFG-1,HMFG-2, SM-3 and SM-4 and displayed by polyacrylamide gelelectrophoresis and fluorography (FIG. 9). Two proteins of about 68 kdand 92 kd were immunoprecipitated by SM-3 (lane 2) and SM-4 (lane 1). Itwas also found that HMFG-1 (lane 4) and HMFG-2 (lane 3)immunoprecipitated these proteins; however, no bands in these areas wereprecipitated by an irrelevant monoclonal antibody to human interferon(lane 5). The fact that HMFG-1 and -2 immunoprecipitated these proteinswas an unexpected finding as it was previously thought that these MAbsrecognize carbohydrate determinants (1). However, we also found thatHMFG-1 and -2 react very strongly with the fully stripped, iodinatedcore protein (20). These results together with the MAb reactions on theβ-galactosidase fusion proteins (see below) confirm that the epitopesfor HMFG-1 and -2 are, at least in part, protein in nature.

The abundance of the core protein mRNA in total cellular poly(A)⁺ RNAwas 4% as estimated by comparing the amount of (³⁵ S)methionine presentas immunoprecipitated protein to the amount of methionine incorporatedinto total protein during in vitro translation.

Screening of the cDNA library

The λgt11 cDNA library made from size selected MCF-7 mRNA (see Methods)was screened initially with the polyclonal antiserum made to the mucincore protein which had been stripped of its carbohydrate. Screening of2×10⁶ plaques resulted in 11 positive clones, 7 of which were takensuccessfully through two further rounds of plaque purification.

To demonstrate that the reactivity of the phage clones with the antibodyprobes was due to antigenic determinants on the cDNA translationproduct, β-galactosidase fusion proteins were made from all 7 clones.The proteins were separated by electrophoresis, transferred tonitrocellulose paper and probed with a variety of antibodies to thestripped mucin, including the polyclonal antiserum which was usedinitially to select the clones and a cocktail of SM-3 and SM-4. Inaddition, HMFG-1 and HMFG-2, the two monoclonal antibodies whichoriginally detected this differentiation and tumor-associated epithelialmucin (1, 14) were tested. All 7 clones yielded fusion proteins whichwere specifically recognized by the polyclonal antiserum, the monoclonalcocktail, and HMFG-2. HMFG-1 antibody reacted with 6 of the 7 fusionproteins and failed to recognize the protein from clone 9 which containsthe smallest insert. In every case the strongest signal was given by theHMFG-2 antibody and this reaction is shown in FIG. 10. Monoclonalantibodies to keratins and to a carbohydrate epitope on this fullyglycosylated mucin were used as controls and showed no reactivity. Amonoclonal antibody to β-galactosidase was a positive control and theband recognized correlated in every case with the band recognized by thespecific antibodies. The sizes of the fusion proteins varied inproportion to the sizes of the cDNA inserts found in the bacteriophage.

Characterization of cDNAs and RNA blot analysis

The inserts from the A clones were designated pMUC3-10 (omitting pMUC5)and were subcloned into the vector pUC 8 for easier manipulation. The 7clones were compared to each other for sequence homology. Each of theplasmids was digested with EcoRI and the insert separated on a 1.4%agarose gel. The largest cDNA insert from pMUC10 was used to probe theinserts and found to hybridize to all 6 inserts (FIG. 11). pMUC 7 wasfound to contain two inserts following digestion with EcoRI; however,only i of the inserts hybridized to the pMUC10 probe. The insert bandswere not derived from phage DNA since the pMUC10 probe did not hybridizeto Hind III-digested λ phage DNA.

As shown by agarose gel electrophoresis (FIG. 11), the inserts vary insize from about 200 to up to about 1800 bp. The largest insert frompMUC10 has been used as the hybridization probe in all subsequentexperiments.

Because the λMUC clones were identified only by antibody binding, weneeded additional assurance that they were indeed coding for the breastepithelial mucin. To determine the authenticity of pMUC10, we correlatedthe presence of mRNA hybridizing to the clone with mucin expression invarious cell lines. As shown in FIG. 12, the cDNA hybridized to twotranscripts of 4.7 kb and 6.4 kb in the RNA from the breast cancer celllines MCF-7 and T47D which were shown previously to express the HMFG-2antigen (1, 14). Significantly, the pMUC10 probe hybridized totranscripts of approximately the same size in RNA extracted from normalmammary epithelial cells cultured from milk (42). A third band of 5.7kbcan be seen in the RNA from these normal cells. In contrast, three humancell types that lack the mucin, breast fibroblasts, Daudi cells andHS578T, a carcinosarcoma line derived from breast tissue (43), showed nodetectable pMUC10-related mRNA. The 6.4 kb band appears to be the mostabundantly expressed. The presence of at least two sizes of mRNA fromMCF-7 cells correlates with the immunoprecipitation of two proteins of(molecular weights 68 kd and 92 kd) from in vitro translated mRNA fromMCF-7 cells. The normal mammary epithelial cells were derived frompooled milk samples and the additional transcript observed may be due topolymorphisms among individuals.

Genomic DNA blot hybridization and detection of a restriction fragmentlength polymorphism (RFLP)

Genomic DNA was prepared from a panel of ten individuals consisting ofsix unrelated individuals and a family of four, and from three celllines. The DNAs which were digested with HinfI or EcoRI and blotted andhybridized to the radiolabelled pMUC10 insert, exhibit restrictionfragment length polymorphisms. The restriction fragments from the tenindividuals and three cell lines are shown in FIG. 13. The patternconsists of either a single band or a doublet of sizes ranging from3400bp to 6200bp in the HinfI digest (with the exception of the ZR75-1DNA in lane 12, FIG. 13A which shows three bands) or from 8200bp to9600bp in the EcoRI digest (FIG. 13B). There appears to be a continuousdistribution of the fragment sizes which implies a high in vivoinstability at the locus. The pattern of fragments observed in thefamily of four (lanes 1-4) suggests that these fragments are allelic.Preliminary studies of the DNA made from white blood cells of normal,related individuals indicate the existence of a number of independentalleles with an autosomal codominant mode of inheritance. These studieswill be the subject of a separate investigation.

Discussion

The cDNA clones described here which were obtained from the MCF-7 λgt11library were selected using polyclonal and monoclonal antibodiesprepared against a normal cellular product, the milk mucin in itsdeglycosylated form. This was done because it was easier to obtain largequantities of the mucin for stripping than to prepare similar quantitiesof immunologically related glycoproteins expressed by breast cancercells (44). The fact that the antibodies did select for cDNA coding fornonglycosylated core protein molecules in MCF-7 cells, strongly suggeststhat the glycoproteins in these cells, which were originally detected bytheir reaction with antibodies to the milk mucin, contain the same coreprotein as this mucin. This is confirmed by the detection of mRNAs ofapproximately the same sizes in the normal and malignant cells, usingone of the probes isolated from the MCF-7 library. We will thereforerefer to the antibody reactive glycoproteins on breast cancer cells asmucins, bearing in mind that their processing may be different resultingin molecules of different molecular weights but with the same coreprotein as that of the milk mucin.

Seven clones were obtained from the MCF-7 library of which the largestwas 1800kb. This clone cross-hybridized with the other 6 smaller clones.The β-galactosidase fusion proteins expressed by six of thecross-hybridizing lambda clones were reactive with the polyclonalantiserum directed against the mucin core protein as well as with fourwell-characterized monoclonal antibodies directed to various epitopes onthe stripped core protein, SM-3, SM-4, HMFG-1 and HMFG-2 (14, 20). Thesmallest lambda clone, kMUC9, produced a β-galactosidase fusion proteinwhich reacted with three of the four monoclonal antibodies and with thepolyclonal antiserum.

The surprising result that the extensively characterized HMFG-1 andHMFG-2 monoclonal antibodies reacted strongly with the lambda plaquesand the fusion proteins and could immunoprecipitate proteins from invitro translated mRNA provides strong evidence that these clones doindeed code for a portion of the mucin core protein. Although previousevidence such as resistance to fixation, boiling, treatment withdithiothreitol and NaDodSO₄ and the presence of multiple epitopes on themolecule suggested that these were carbohydrate (1), it has not beenestablished that the epitopes of the HMFG-1 and HMFG-2 monoclonalantibodies are definitely protein in nature. Carbohydrate may berequired to obtain the strongest binding, either as part of the epitopeor by conferring some conformational change on the protein portion, butpart of the antigenic determinant must consist of an amino acidsequence. Since these two MAbs are reactive with the fully glycosylatedmilk mucin as well as the stripped core protein, this data means thatthe intact molecule contains areas of naked peptide which contribute tothe antigenic sites for these two antibodies.

Confirmatory evidence that pMUC10 codes for the mammary mucin coreprotein is provided by RNA blots. The relative abundance of mRNA in thebreast cancer cell lines MCF-7, T47D, ZR-75-1 and in normal mammaryepithelial cells corresponds to the antigen expression by these cells asmeasured by the binding of the HMFG-1 and HMFG-2 monoclonal antibodies.Cell types which are negative for antigen expression such as humanfibroblasts, Daudi cells and HS578T, a carcinosarcoma line derived frombreast (14), are negative in RNA blot hybridizations. A fortuituousobservation made with the ZR-75-1 cells yielded indirect strong evidencethat pMUC10 does indeed code for the mucin glycoprotein core protein.This cell line, which routinely expresses large amounts both of mRNA andantigen, yielded one preparation of RNA which was unexpectedly negativeby blot hybridization. It was subsequently found that those particularZR-75-1 cells from which the RNA had been made had lost the expressionof the antigen as well at this time (as determined by reaction withHMFG-1 and 2). Different passage numbers of the ZR-75-1 cells wererecovered and shown once again to express both antigen and message. Thesizes of the messages, 4.7 kd and 6.4 kb, are quite large, since a 68 kdor 92 Kd protein would need only about 3 kb to code for the proteinportions. This suggests that a large portion of the mRNA maybeuntranslated. Efforts are underway to obtain a full-length clone.

Thus, the cDNA clones presented here represent a portion of the genecoding for the human mammary mucin which is expressed by differentiatedbreast tissue as well as by most breast cancers. The major proteinsprecipitated from in vitro translation products of RNA from MCF-7 cellsby antibodies to the milk mucin core protein (68Kd) have an apparentmolecular weight of 68Kd and 92Kd. These proteins, produced by thebreast cancer cell therefore share epitopes with the 68Kd core proteinof the milk mucin (20). Whether a similar 92Kd protein is also producedby normal mammary epithelial cells, and is truncated or destroyed by HFtreatment is not yet clear. MCF-7 cells biosynthetically labelled with14C amino acids yield upon immunoprecipitation with HMFG-1 and HMFG-2antibodies, two glycosylated proteins of 320 kd and 430 kd and it ispossible that each of these glycoproteins utilizes only one core proteinof either 68Kd or 92Kd. Alternatively, each of the glycoproteins couldcontain both the 92Kd and 68Kd proteins either in different proportionsor variably glycosylated. Further screening of the library may yieldfull length cDNAs coding for both sizes of the immunologically relatedcore proteins. Since there appears to be only a single gene (based onSouthern blot data obtained by using a partial cDNA probe), it isprobable that the multiple messages arise by alternative RNA splicingand this would explain the fact that they contain common sequences.Although a core protein of 68 kd appears to be small to yield a fullyglycosylated molecule of greater than 300 kd which contains 50%carbohydrate, there is evidence that such a structure for mucins ispossible. Ovine submaxillary mucin has a reported molecular weight of1×10⁶ daltons (45), yet its protein core consists of 650 amino acidsresulting in a molecule of 58 kd (46).

The mucins which are detected with HMFG-1 and HMFG-2 MAbs on immunoblotsof tumors and breast cancer cell lines show variations in size from 80kd to 400 kd in the molecular weights of the tumor mucin molecules (1,47). Using these same antibodies which detect high molecular weightmucins present in normal urine, a polymorphism has indeed been shown tobe genetically determined (48). Although the very low molecular weightcomponents are likely to represent precursor forms of the mucin whichappears to be incompletely processed in many tumor cells (20), thevariations in the higher molecular weight components are likely to bedue to this genetic polymorphism. It was unclear, however, whether thestructural basis of the polymorphism was due to the geneticallydetermined protein or to the carbohydrate portion of the mucin. Thedetection of restriction fragment length polymorphism in the Southernblotting experiments using the mucin probe suggest that the mucinpolymorphism occurs at the level of the DNA which codes for the protein.Preliminary sequence data suggest that the basis for this polymorphismis a region of variable tandem repeats present in the protein codingsequences. This structural feature may be responsible for the generationof the many allelic restriction fragments at the mucin locus. We arepresently investigating the basis of the mucin polymorphism by aSouthern blot survey of DNA from white blood cells of normal, relatedindividuals whose inheritance pattern of urinary mucins has beendetermined. In addition, we are examining DNA preparations made from thewhite blood cells and tumors of individual breast cancer patients todetermine if there is any discordance between genotype in the pairedsamples, since tandemly repeated DNA may provide an unstable site whererecombination or amplification could occur.

The presence of mucins in the majority of carcinomas and theirassociation with the differentiation of mammary epithelial cells makesit particularly important to identify regions involved in the tissuespecific and developmental regulation of the gene. Moreover, theintroduction of a functional mucin gene into cells should provideinsights into the role of this molecule in breast epithelialdifferentiation and possibly enable us to identify any alterations inthe function or expression of the mucin which are related to malignanttransformation in the human breast.

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We claim:
 1. An antibody, or an epitope-binding fragment of an antibody,which binds to a peptide epitope of the core protein of human mammarypolymorphic epithelial mucin glycoprotein, wherein said core protein isthat which is bound by the reference antibody SM3, secreted by hybridomacell line HSM3 (accession number ECACC 87010701), and wherein saidantibody or fragment binds to said glycoprotein as secreted by humanmammary epithelial tumor cells and does not bind to said glycoprotein assecreted by the normal lactating human mammary gland.
 2. An antibody, oran epitope-binding fragment of an antibody, which binds to a peptideepitope of the core protein of the human mammary polymorphic epithelialmucin glycoprotein, which epitope is also bound by the referenceantibody SM3, secreted by the hybridoma cell line HSM3, deposited withthe European Collection of Animal Cell Cultures under accession numberECACC
 87010701. 3. The antibody of claim 2, which is an intact antibody.4. The antibody or fragment of claim 3, which is reference antibody SM3,secreted by the hybridoma cell line HSM3, deposited on Jan. 7, 1987 withthe European Collection of Animal Cell Cultures under accession numberECACC 87010701, or an epitope-binding fragment thereof.
 5. The antibodyof claim 4, which is an intact antibody.
 6. The antibody or fragment ofclaim 2, which does not bind to intact, human mammary polymorphicepithelial mucin glycoprotein as secreted by the normal lactating humanmammary gland.
 7. The antibody or fragment of claim 2, which isdetectably labeled.
 8. The antibody of claim 7, which is an intactantibody.
 9. The antibody or fragment of claim 2, which is a monoclonalantibody or an epitope-binding fragment thereof.
 10. A hybridoma cellwhich secretes a monoclonal antibody according to claim 9 underculturing conditions.
 11. The hybridoma cell of claim 10, which isdesignated HSM3, deposited on Jan. 7, 1987 with the European Collectionof Animal Cell Cultures under accession number ECACC 87010701, or asubclone thereof which has all of the identifying characteristics ofsaid hybridoma.
 12. A method of diagnosing cancer in a human or animal,which comprises the steps of:(a) administering to a human or animal, orto a sample obtained from a human or animal, a diagnostically effectiveamount of an antibody or an epitope-binding fragment thereof, whichantibody or fragment binds to an epitope of the core protein of humanmammary polymorphic epithelial mucin glycoprotein, which core protein isalso bound by the reference antibody, SM3, secreted by hybridoma cellline HSM3, which hybridoma has the accession number ECACC 87010701, andwherein said antibody or fragment binds to said glycoprotein as secretedby human mammary epithelial rumor cells and does not bind to saidglycoprotein as secreted by the normal lactating human mammary gland;(b) determining whether said antibody or fragment is bound to saidepitope; and (c) diagnosing the presence or absence of cancer as aresult of said determination.
 13. The method of claim 12, wherein saidantibody is a monoclonal antibody secreted by hybridoma cell line HSM3,which hybridoma has the accession number ECACC 87010701, or anepitope-binding fragment thereof.
 14. A method of diagnosing cancer in ahuman or animal which comprises the steps of:(a) administering to ahuman or animal, or to a sample obtained from a human or animal, adiagnostically effective amount of an antibody or an epitope-bindingfragment thereof, wherein said antibody or fragment binds to an epitopeof the core protein of human mammary polymorphic epithelial mucinglycoprotein, which epitope is also bound by the reference antibody SM3,secreted by the hybridoma cell line HSM3, deposited with the EuropeanCollection of Animal Cell Cultures under accession number ECACC87010701; and (b) determining whether said antibody or fragment is boundto said epitope; and (c) diagnosing the presence or absence of cancer asa result of said determination.
 15. The method of claim 14, wherein saidantibody is a monoclonal antibody secreted by hybridoma cell line HSM3,which hybridoma has the accession number ECACC 87010701, or anepitope-binding fragment thereof.
 16. The method of claim 14, in whichthe antibody is an intact antibody.
 17. The method of claim 14, in whichthe antibody or fragment does not bind to intact, human mammarypolymorphic epithelial mucin glycoprotein as secreted by the normallactating human mammary gland.
 18. The method of claim 14, in which theantibody or fragment is detectably labeled.